The Chicago Cubs struck early this winter with a quick signing of Tyler Chatwood, a starter who has never qualified for the ERA title in his career. They signed him to a three-year, $38 million deal, reflecting at least in part the importance that Statcast data plays in teams' decisions on which players to acquire and at what cost.

Chatwood was the clear No. 4 starter in their rotation, with Jose Quintana their No. 1, followed by Jon Lester and Kyle Hendricks in either order, and a cast of several potential starters for the final spot. Rather than adding another back-end starter, the Cubs decided to take advantage of the soft market for top-end free agents by signing the best player still available, Yu Darvish, at what appears to be a bargain salary on a deal that's a year or two too long.

Darvish's 2017 season ended as poorly as possible, with claims that the Astros hitters noticed that he was tipping his pitches and mumbling about Darvish's lack of toughness, but that shouldn't obscure his very good regular season performance. His 186 ⅔ innings and 3.8 WAR would both have led the Cubs, and his strikeout rate of 27 percent would have only ranked behind Quintana's. None of the Cubs' internal candidates for the open rotation spot projected to be worth a win or more above replacement, and that's assuming that the Cubs immediately hit on the best candidate and gave him 25 starts. Now their rotation is set as long as these five starters are healthy, and erstwhile starters like Mike Montgomery and Eddie Butler can go to the bullpen full-time, where, as two-pitch guys, they should be more effective.

Darvish isn't a pure ace any more, not by an objective standard (as opposed to simply saying a team's best pitcher is an ace), in part because he's changed how he pitches since his return from Tommy John surgery. He overuses his cutter now, while barely using his splitter or changeup and not employing his slider enough. The new mix has left him too vulnerable to left-handed hitters, especially since he doesn't like to throw the cutter in on lefties' hands, so they can lean out over the plate more and get to his four-seamer. His arm strength is still there, and the slider still shows plus, so I think he has some untapped potential right now. He's averaged 4.5 WAR per 31 starts over his entire MLB career, and if he even got to 80 percent of that the Cubs would probably be thrilled, given his $21 million/year average salary.

Six years is too long for any free agent starter, and the deal takes Darvish through his age-36 season. Three more healthy seasons as a starter would put Darvish second among Japanese-born starters in innings pitched and games started in MLB. Japanese pitchers pitch a lot when young, more than comparable American pitchers do today in our pitch count-conscious environment, and I wonder -- without enough data to prove or disprove the concern-- if Darvish will be less durable in his 30s than starters who didn't come up through NPB. Darvish has an opt-out, but if he gets hurt or loses effectiveness before that date, the Cubs will be on the hook for the whole deal.

The Brewers have to feel a bit gut-punched to see Darvish, a pitcher they'd targeted, go to a division rival, increasing the gap between them and the Cubs just a few weeks after they'd added two outfielders to try to get closer to the defending NL Central champs on paper. I think this puts pressure on Milwaukee and the Cardinals to look for further rotation help via trade or free agency, with Jake Arrieta the only comparable arm left in free agency and only a few 3- or 4-win arms even possibly available in trade. The Cardinals do have the depth to pull off a deal for someone like Chris Archer, though, given their surplus in outfield and starter pitching prospects.